Well, when I could not reach any of my Tax clients I needed to obtain more info from, so I played with some chainsaw carb … just could not help myself!
On my first attempt, I learned what not to do, but luckily the second attempt seems to have worked.
The first pic is a ZAMA made Walbro style carb stock (purchased from D Dave). The venture is a little smaller than the real Walbro carbs, but otherwise they work well. I'm pretty sure the tighter venture is limiting the RPMs of my Ported Asian 440 Big Bores.
On my first attempt, I opened up the venture approximately .025 and also tried to modify the fuel nozzle by slimming both sides - a mistake! The saw did not want to idle unless I made the Lo very rich. Then, when I tried to accelerate, it fell on it's face unless I richened up the Hi. When I richened the Hi it would not rev (was way too rich). Played with various tunes for a while, but it was a catch 22!
I did not realize (till I ground it) that the fuel delivery nozzle has a wider opening near the end, and a smaller opening higher up. By breaking through the walls of the wider opening, I screwed things up. I will likely try to file it down all the way across and see if I can save it, but for now I just pulled out another carb.
So on the next carb I just opened up the venture and left the fuel nozzle alone. It seems like I may have achieved success! The saw idled well, accelerated well and definitely hit higher RPMs than I did before.
I was stoked and ready to put it in some wood when the wife comes out yelling at me not to disturb everyone in the neighborhood with my saw on Easter! Women ... they don't understand anything that's important!
Hopefully I will get the time to put it in some wood tomorrow and see how it does. I'm optimistic, but know better than to make predictions before I actually test it! I modded a muffler once on a 660 and it piss revved fantastic, faster throttle response, higher RPMs, but when I put it in wood it fell on it's face!
Original Carb, 1st attempt, 2nd attempt.
Attached Files:
. I left the lower split portion uncut and the stump, his dad does some carving and wanted them that way. We tried to save out a nice log, but it was cracked so they just had me cut it up too.
